gh-121192: Add fast path to deepcopy() for empty list/tuple/dict/set

Lib/copy.py

@@ -126,10 +126,13 @@ def deepcopy(x, memo=None, _nil=[]):
     if cls in _atomic_types:
         return x
 
-    d = id(x)
     if memo is None:
+        if cls in _builtin_iterables and not x:
+            return cls()
+        d = id(x)
         memo = {}
     else:
+        d = id(x)
         y = memo.get(d, _nil)
         if y is not _nil:
             return y
@@ -173,6 +176,7 @@ def deepcopy(x, memo=None, _nil=[]):
 _atomic_types =  {types.NoneType, types.EllipsisType, types.NotImplementedType,
           int, float, bool, complex, bytes, str, types.CodeType, type, range,
           types.BuiltinFunctionType, types.FunctionType, weakref.ref, property}
+_builtin_iterables = {tuple, list, dict, set, frozenset}
 
 _deepcopy_dispatch = d = {}
 

Misc/NEWS.d/next/Library/2024-07-01-00-32-33.gh-issue-121192.RZFhQP.rst

@@ -0,0 +1,2 @@
+Add fast path to :func:`copy.deepcopy` for empty lists, tuples, dicts, sets
+or frozensets.